Rechargeable battery systems for electric vehicles with a purely electric drive and for hybrid vehicles and vehicles with fuel cell drive are the subject of current research. At present, in the said types of vehicle, lithium-ion batteries are preferably used, which are distinguished by a high energy density and an only slightly marked, undesired memory effect. The capability of a rechargeable battery to reliably supply various electric consumers installed in motor vehicles with electrical energy depends to a considerable extent on the thermal conditions prevailing in the environment of the battery. This is because both the electrochemical processes occurring in the battery in the provision and also in the receiving of electrical energy—in the sense of recharging—are dependent to a not insignificant extent on the operating temperature of the battery. Extensive investigations of various lithium-ion-based battery systems have shown, for instance, that below a critical temperature, for instance in the region of approximately 0° C., the electrical energy density made available by the battery decreases greatly compared with higher operating temperatures. Below this temperature, in addition damage to the Li-ion cell can occur during charging.
The provision of thermally well-defined environmental conditions is therefore crucial for a reliable and interference-free operation of said batteries—this applies not only for said lithium-ion-based batteries, but generally for any rechargeable battery systems. With regard to the considerable temperature fluctuations occurring under normal operating conditions for instance in a motor vehicle, this means that these must be compensated by suitable temperature control devices coupled thermally with the battery, in order to keep the environmental temperature of the battery—and hence also the temperature of the battery itself—within a temperature interval specified, for example, by the manufacturer.
Temperature control devices with heat exchangers are known from the prior art, which are based for example on fluid ducts in the form of cooling plates or collector/tube systems which form a cooling channel, which is flowed through by a heat transmission medium, for example a coolant. The battery cells which are to be temperature-controlled are brought to lie respectively flat against at least one duct wall of the heat exchanger of the temperature control device. In this way, a thermal contact is produced between the battery and the coolant, so that the coolant can extract heat from the battery cells and their temperature can consequently be kept below a maximum permissible threshold value.
In such temperature control devices, it proves to be significant, however, that both for the duct walls of the fluid ducts, and also for the housing, a material with high thermal conductivity must be selected, if a highly effective thermal coupling is to be achieved between battery and coolant. Metals which have the desired characteristics with regard to the thermal conductivity therefore come into consideration to a particular extent. If, however, a metal is selected as material for a heat exchanger of the temperature control device cooperating with the battery or respectively for the battery housing, then an electrically conducting connection also occurs between the heat exchanger and the battery,—which connection is undesired for safety considerations —, when these two components are brought mechanically in contact with one another. Such an electrical connection could be avoided if the heat exchanger were arranged at a sufficient distance from the battery. However, owing to the air gap then present, this would lead to an unacceptable reduction of the thermal coupling between battery and heat exchanger.
For an effective thermal coupling between battery cells and heat exchanger with simultaneous electrical insulation of the two components with respect to one another, it is therefore usual to provide a thermal interface with electrically insulating characteristics between these two components. From DE 10 2008 059 952 B4 a battery with several battery cells and a generic temperature control device constructed as a cooling device for cooling the battery cells is known. A metallic base body of the temperature control device is equipped with an electrically insulating insulation layer. This is an injection moulded layer of a plastic injected onto the base body.
It is further known from the prior art to arrange thermally highly conductive materials with elastic characteristics between the individual battery cells and the temperature control device. These are able to compensate the formation of undesired intermediate spaces between individual battery cells and the duct walls of the fluid duct, caused for instance owing to manufacturing or installation tolerances. Heat-conducting foils, heat-conducting pastes or heat-conducting adhesives are used for use as a conventional thermal interface between the battery cells and the duct wall.
It proves to be a problem in the said heat-conducting pastes that their function in the practical operation of the temperature control device, typically in a motor vehicle, cannot be guaranteed for instance owing to regularly occurring vibrations. The mentioned heat-conducting foils, on the other hand, have the disadvantage that they are expensive to purchase and their bubble-free application on the temperature control device is complex with regard to the technical process. In addition, owing to their only limited elastic deformability they can only compensate to a limited extent variations in the dimensions of the intermediate spaces between the temperature control device and the individual battery cells.
It is therefore an object of the present invention to provide an improved embodiment for a temperature control device, in which the problems discussed above no longer occur.
The said object is solved by the subject of the independent claims. Preferred embodiments are the subject of the dependent claims.